Thanks for all the great responses. I definitely feel more educated on the subject. Is the issue of a tire blow out because of braking heat a real issue? I understand that it has happened, but is there evidence that it happens often? I mean, tires blow out on aluminum clinchers as well, what makes them any safer?

Tubules aren't really an option for me. I don't race and do most of my riding on weekends, so a clincher makes more sense for me. I also ride in an area that's mainly flat, so braking is minimal. I would love to try carbon clinchers, and being a designer bling does play a factor, but function is also important.

What about the Mavic Cosmic Carbone 40C? Seems like they might have solved the heating/blowout issue with the aluminum core. They're expensive, but would you get them if they cost a third of the price?

I would love to try carbon clinchers, and being a designer bling does play a factor, but function is also important.

I can understand that, full carbon clinchers look nice, but you end up spending a lot of money to get an inferior product (compared to carbon tubulars). IMHO it's either alu clinchers (for everyday training) or carbon tubulars (for racing or recreation riding).

The problem with carbon clinchers lies in heat transmission and retention. The beauty of an aluminum rimmed clincher lies with aluminum's inherent heat dissipation properties. Aluminum doesn't retain heat very well. Put an aluminum pan on a stove, heat it up, turn off the heat and the pan cools down quickly. That's why professional cooks use stainless (better heat maintenance). Although aluminum's heat retention is bad for cooking, it's great for cycling.

Carbon is more like steel in that sense: carbon will retain heat far longer than aluminum. As the carbon heats up and doesn't dissipate it very quickly, the resin which bonds the material together can breakdown. Also, the more heat that's built up, the less effective your brakes are. That's why if you are riding in flat areas, where the stops are relatively short, the wheel doesn't have time time to build up heat. Personally, I've even ridden in some mild hilly areas (Central Texas), and haven't had a worry about the build up. That being said, I do keep a set of aluminum clinchers, given my weight and size, for use in really hilly rides. However, 99% of the time, I'm on my CF clinchers (formerly Reynolds DV3K's, now Zipp 303's).

Is there a benefit to a carbon clincher? Absolutely. Asthetics aside, carbon clinchers are generally lighter than their aluminum brethren (when comparing equal size wheels). Aluminum, although light, is not strong. Pound for pound, CF is stronger than aluminum (and steel, for that matter). To match the strength needed to make a wheel, builders have to resort to a couple of different options: either use more material (weight) or exotic alloys (cost).

Personally, I have never tried Mavic wheels. Some love them, some hate them. I'm indifferent. I can, however, tell you two things: first, there seems to be an issue mounting tubeless tires to them (see my comment below on tubeless). Second - and this has nothing specific to Mavic - I recently switched over to the wider rim width, and I will never go back. The wider contact patch is noticeable, and provides a more stable footing. Also, the tires seem to absorb a little more impact than my old narrow wheels. Since Mavic hasn't embraced the wider rim mantra, they're off the table for me (for the moment).

Now, if blowouts are your primary concern, I offer an alternative to you: tubeless tires. Almost any clincher wheel can be converted (using tubeless specific tires - standard road clinchers are NOT recommended for the conversion, due to tire pressures), and the very nature of the tire's locking bead is to prevent the tire from ever coming off the rim. Personally, I need two tire levers to make the initial removal of the tire off the rim. Yes, they are more complicated to setup than a standard clincher, however, when on the road, if you do suffer a flat (as everyone from a clincher to a tubular will tell you, does happen), you can treat the tire like a clincher and just put a tube in the wheel and ride on. Is it messier than a clincher? Yes - there is usually sealant in the tire, that prevents/seals smaller leaks - however, you eliminate the tube (weight savings), have a lower tire pressure (more comfort), eliminate the risk of pinch flats, and have minimal downtime during a flat, compared to swapping out a tubular tire.

Don't let the people that worship the tubular gods fool you. If you are planning on racing on tubular's you really can't train on them or you risk racing on a tire that should have been replaced because there is a little too much wear on the tread. And if you do decide to replace your tires often during race season then you have to find away to peel of the slightly used tires with out damaging them so that you can remount them to train when a flat is not going to ruin your race. I don't like getting flats in races, yes you can get a free lap but you now are on a less desirable wheel, unless you can afford to have a second set of carbon's in the pit. Race rubber wears quickly, I always replace the rear tire mid season. You need to learn how to glue them on properly or pay someone that knows what they are doing. Don't leave them in the back of your car in the sun when you stop for lunch on the way to that race or risk melting the glue. So if you compare apples to apples, Open CX's or Veloflex clinchers with the equivalent tubular, the tubular is slightly lighter and very slightly better ride. Don't buy cheap rims and you will never have a problem. I have ridden nothing but carbon clinchers for at least the last five years and hate every year when winter rolls into Chicago and I switch to regular wheels until the salt and snow goes away. So if you want a race only wheel there is a small gain from tubulars, but that comes with a cost.

Living in flat Denmark, I switched to Carbon Clinchers three years ago. I will never go back. My bike is under the UCI limit with my Enve 6.7 Clinchers anyway. I do have a pair of Enve 1.25 tubular, that I sometimes use in hilly races, but I like the 6.7's better.

The aluminium rim conducts heat away from the braking surface. The heat is spread through the entire rim rather than being concentrated on the braking surface. This means that the hottest parts of the rim do not get so hot. The rest of the rim is a heat sink. It can then radiate and convect heat to the air.

Carbon fiber composite does not conduct heat as well as aluminium (or steel). The braking surface will be hotter and the body of the rim cooler for the same heat input to the braking surface. This is bad for two reasons- there is less rim area to radiate and convect heat away from the rim, and worse, epoxy has a rather low (compared to aluminium) temperature at which heat changes its physical properties. The epoxy goes soft. I have seen figures as low as under 200 degrees f. While aluminium is fine to 600 or more.

The normal mode of overheating failure on a CF clincher is the brake tracks start bulging in spots where the epoxy is softening. That makes the brakes grab harder there increasing the heat to that spot. If you keep going the rim will deform enough (due to the tire pressure pushing the rim walls apart) that the tire blows off the rim.

With aluminium rims the mode of overheating failure is usually the tube rupturing from overheating.

CF rim makers have been using higher temp epoxies to resist heat and surface treatments to keep heat from the rest of the rim (i.e. FarSport's basalt). They're better than they were just a few years ago. The manufacturers also work on brake pad compounds which put less heat into the rim. Which is why you should use the pads recommended by your rim maker.

It's not big descents per se that are risky on CCs, it's technical descents. While stopping from 55 mph does put a lot of heat into the rim, on a wide open descent you don't have to do that. Where on a steep descent with many tight corners you may only hit 35 mph but are braking to 15 or 20 repeatedly. That'll put more heat into the brakes than a big fast non technical descent, due to the more frequent braking and the slower speeds reducing heat convection from the rims. Of course descending skill comes into play, as the faster you are the less you brake. The only place I have had a problem with CC rims is on a very steep very technical road, on a very hot day. I've used them in the Everest Challenge and Death Ride which have very long 55mph descents that go down 3000-6000' but not a lot of turns that I need to brake hard for.

On the other side the performance gain is small. And the braking is not as good as aluminium. So I use them for races but train on aluminium rims.

Tubulars are great if you are competent at changing them on the road. Also carrying a spare tubular pretty much negates the weight advantage over clinchers and rolling resistance is a wash between good tubulars and clinchers. Many of the races I do are in the middle of nowhere and have spotty or no support. Since I'm not good at changing tubulars on the road I use clinchers.

What about the Mavic Cosmic Carbone 40C? Seems like they might have solved the heating/blowout issue with the aluminum core. They're expensive, but would you get them if they cost a third of the price?

Yes.

I have Enve 3.4 clinchers and 2013 CC SLR clinchers that I raced on all year. The new Exalith brake track is terrific, braking noise reduced after the 'holes' filled in (as Mavic state happens) and you get alu braking on a carbon rim that looks like a full carbon clincher and is not too much heavier than same depth offerings.

If those 40C were available 12 months ago when I was looking at my Mavic wheel options (they were my team's wheel sponsor, but we still paid for our wheels) then I would have gone them.

That said, having had 6.7 and (still have) 3.4's I am impressed with the SLR's. In spite of them not having the new 'wide rim' profile.

What about the Mavic Cosmic Carbone 40C? Seems like they might have solved the heating/blowout issue with the aluminum core. They're expensive, but would you get them if they cost a third of the price?

Yes.

I have Enve 3.4 clinchers and 2013 CC SLR clinchers that I raced on all year. The new Exalith brake track is terrific, braking noise reduced after the 'holes' filled in (as Mavic state happens) and you get alu braking on a carbon rim that looks like a full carbon clincher and is not too much heavier than same depth offerings.

If those 40C were available 12 months ago when I was looking at my Mavic wheel options (they were my team's wheel sponsor, but we still paid for our wheels) then I would have gone them.

I just got them for less than half the retail price, brand new. Just the wheels and 6 spokes, though. They don't come with the tires, tubes, bags and skewers. Still a great deal.

I may have missed this in this thread, but what's the perspective on "hybrid" carbon rim/aluminum brake track as in some Easton wheels? I'm not in the market (alloy works fine for me) but someone I know just bought a set; hence the question

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